Binding M-<up> / M-<down> in Emacs 23.1.1

Question

I'm trying to put in a feature that I miss from Eclipse, where Alt+[Up/Down] transposes the lines up or down, but can not for the life of me figure out how to assign to these keys properly. I am using it in -nw mode (so just in a shell window), and typically run in a screen session.

Using a global key binding, I can get it to work with letter combinations, like (kbd "M-m"), but every combination I have tried for the arrow keys just gives me a message that doesn't make sense, I always get:

"ESC <up> is undefined"

What I have tried:

(global-set-key (kbd "M-<up>") 'transpose-line-up)    
(global-set-key (kbd "<escape>-<up>") 'transpose-line-up)
(global-set-key [M-up] 'transpose-line-up)
(global-set-key [\e \M-O A] 'transpose-line-up)

And C-h c just returns:

ESC <up> (translated from ESC M-O A) is undefined

None of these work, either using ESC or Alt.

Any idea how I can make this work? I would prefer to have these as Alt+[Up/Down] just because that is what I am used to.

Edit

From the comments:

• C-q Up prints ^[OA.

• C-q M-Up prints ^[ and moves the cursor up a line.

• C-h k (Alt+Up) prints ESC <up> (translated from ESC M-O A) is undefined.

Thanks for the suggestions, but they all turned out the same.

Answer 1

Emacs has a complex mechanism to handle the vicissitudes of function key and modifier encodings on various terminal types. It doesn't work out of the box in all cases. The following settings should work on your terminal:

(define-key input-decode-map "\e\eOA" [(meta up)])
(define-key input-decode-map "\e\eOB" [(meta down)])
(global-set-key [(meta up)] 'transpose-line-up)
(global-set-key [(meta down)] 'transpose-line-down)

You should be able to use (kbd "<M-up>") and (kbd "<M-down>") in place of [(meta up)] and [(meta down)], as long as you've done the step of telling Emacs (via input-decode-map) about the escape sequences that your terminal uses to encode these key combinations.